A primary school principal I once worked with said that if you ask a group of year one girls who the best runner in the class is, they all point to themselves: I'm the best runner, they'll say. Ask a group of year six girls, she went on, and they'll point to the best runner.

Ask a group of year nine girls, I thought to myself, and when they point out the fast girl, she'll flinch and demur, saying, "No, I'm awful!" Pride, after all, is a cardinal sin in girls' social culture. It's a lesson they learn early and with ugly consequences. Act too confident and you'll be isolated, called "conceited," a "bitch," a girl who "thinks she's all that," who's "full of herself."

Girls adapt by learning the language of the humble. They raise their hands tentatively at the elbow, beginning classroom comments with apologies ("I'm not sure if this is right, but . . ."). They turn strong opinions into questions with "upspeak." As Amy Schumer lampooned in her viral sketch, young women deflect compliments with frenetic intensity - or, as I've found in my own research, perform an inverse maneuver, earning a compliment by putting themselves down ("I look so awful today." "No you don't, you look amaze!").

Enter the selfie, which Oxford Dictionaries just picked as its word of the year. As the Pew Center for Internet Research reported earlier this year, 91 percent of teens have posted one. Last week, the first selfie app went live: Shots of Me, backed by Justin Bieber, is a camera app that opens with the lens already facing its user. These days, the selfie and its main outlet, Instagram, generally come in for much adult loathing. But consider this: The selfie is a tiny pulse of girl pride - a shout-out to the self. If you write off the endless stream of posts as image-conscious narcissism, you'll miss the chance to watch girls practice promoting themselves - a skill that boys are otherwise given more permission to develop, and which serves them later on when they negotiate for raises and promotions.

The selfie suggests something in picture form - I think I look [beautiful] [happy] [funny] [sexy]. Do you? - that a girl could never get away with saying. It puts the gaze of the camera squarely in a girl's hands, and along with it, the power to influence the photo's interpretation. As psychiatrist Josie Howard recently told Refinery29's Kristin Booker, selfies "may reset the industry standard of beauty to something more realistic."

I've been an educator for the last 15 years. I do worry that for every girl who posts a selfie with pride, others use it to cobble together the validation they cannot give themselves. I worry also about the girls who spend hours editing out their blemishes and adding filters. A 16-year-old from Texas told me that she longs for the days of their grandmothers' brave, set-in-stone Polaroids. And there is plenty that's troubling about girls' tendency to use Instagram to celebrate their physical appearance over their accomplishments. A survey by the Girl Scouts in 2010 found that girls downplayed their intelligence, kindness and efforts to be a positive influence online in favor of presenting an image that is fun, funny and social.

But I worry more about a world of parents and educators who are overly invested in seeing all social media as problematic, and positioning girls as passive targets instead of agents of their own lives. Every girl is different, and context matters. The selfie flaunts the restrictions of "good girl" culture like a delinquent teen-ager sitting in the back of the classroom, refusing to apologise for what she says. I, for one, want to sit next to her in detention.